Since the first synthesis of metacyclophane by Pellegrin in 1899 and paracyclophane by Cram et al. in 1951, there has been wide interest in these highly strained systems. The restricted positions of the often distorted aromatic rings in these classes of molecules have allowed many studies of the fundamental properties of aromaticity itself. The well-defined topology and high strain of cyclophanes has also found utility in a number of applications including asymmetric catalysis, insulating plastics, and organic electronics. Unfortunately, the field of cyclophane chemistry has been hindered by a lack of high yielding and functional group tolerant preparative methods for their synthesis.
Previous methods to synthesize cyclophanes have relied on intra- and intermolecular macrocyclizations at high dilution and non-ambient temperatures. In many cases, indiscriminant homocouplings such as Wurtz or McMurry couplings are used where a mixture of oligomers and polymer is the primary product. In some more selective cases, Wittig reactions are used to make mixed macrocycles but these cases still rely on unfavorable ring formation. Despite the significant breadth of applications cyclophanes serve in, their synthesis is still confined to synthetic methods devised more than 40 years ago. These regimens, although generally successful, provide little if any selectivity, low yields, and require difficult purifications.